In the modern-day broadband access methods for subscriber line units of the subscriber line of the classical telephone system (xDSL services), connected via coaxial cable (CATV), via broadband radio services (WLAN, UMTS) or satellite communication, a star structure is always present. As a result of the associated concentration of subscriber lines or groups of transmission channels with a plurality of subscribers, the latter disadvantageously affect one another due to spectral interference, in particular in the environment of an intelligent network node which connects the subscriber line units to the backbone of the internet.
Owing to the increasing economic importance of the broadband access methods, numerous methods for improving the attainable transmission speed or data rate of all subscribers have been proposed.
The methods can be subdivided as follows:                A) Algorithms for multiuser detection: The bit sequences of the mutually influencing message transmissions are detected collectively, with the crosstalk relationships being determined simultaneously; see “Multiuser Detection, S. Verdu, Cambridge University Press, London, New York, 1998”. Algorithms of this kind are considered in the UMTS standardization process. As a precondition these algorithms require the message transmissions of all the subscribers involved to be in strict clock-controlled synchronism. This clock synchronicity is categorically not given for xDSL data transmissions and also cannot be implemented technically without considerable changes to the standardized methods and consequently to the hardware equipment used at the subscriber premises and in the exchange (office).        B) MIMO signal processing methods: MIMO systems are understood to mean the mathematical theory for handling systems with vector-value inputs and outputs. MIMO signal processing methods are suitable for improving the aggregate bit rate of a plurality of message transmissions exerting a spectral influence on one another, although a prerequisite is strict clock synchronicity and frame synchronicity of all message transmissions. For the reasons cited in 1.), therefore, the use of MIMO signal processing algorithms such as “MIMO systems in the subscriber-line network, G. Tauböck, W. Henkel in 5th International OFDM Workshop 2000, Hamburg” is not realizable in practice at the present time.        C) Vector modulation methods: Closely related to 2.) are what are referred to as vector modulation methods, described in “Vectored Transmission for Digital Subscriber Line Systems”, G. Ginis and J. Cioffi, published in IEEE Journal Selected Areas of Communications Vol. 20, Issue 5, pp. 1085-1104, June 2002. A significant difference is the a posteriori adaptation of the modulation signal of the individual message transmission systems to the crosstalk transmission functions. As with 2.), strict frame synchronicity and hence clock synchronization of all the modems involved is a precondition for the use of vector modulation methods.        D) Spectrum management methods: As described in “Dynamic Spectrum Management for Next-Generation DSL Systems”, K.-B. Song, S.-T. Chung, G. Ginis, J. M. Cioffi, the aggregate bit rate of all subscribers of a cable group can be maximized by suitable distribution of the spectral power density of the individual subscribers.        
A common feature of all the methods described in the foregoing is that the crosstalk relationships have already been determined at the time of activation of the respective subscriber lines or transmission channels on the subscriber lines.